This application claims the benefit of Korean Patent Application No. 2002-26566, filed May 14, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an office machine, such as a laser printer and a copying machine, and more particularly, to a paper sensing apparatus of an office machine, which is capable of controlling a top margin of a printing paper effectively by exactly sensing a leading end of the printing paper picked up by a pickup roller and conveyed by conveying rollers.
2. Description of the Related Art
An input/output apparatus for performing printing on a medium of printing paper, for example, an office machine, such as an inkjet printer, a laser printer, or a facsimile, generally has a paper sensing apparatus for sensing a leading end of the printing paper to control a top margin of the printing paper.
For example, as shown in FIG. 1, a laser printer 10 includes a paper stacking unit 1 containing sheets of printing paper P therein, a paper conveying unit 2 conveying the printing paper P from the paper stacking unit 1, an image forming unit 6 forming a toner image on the printing paper P conveyed by the paper conveying unit 2, a paper sensing apparatus 30 disposed between the paper conveying unit 2 and the image forming unit 6 to sense a leading end of the printing paper P, a settling unit 7 settling the toner image formed on the printing paper P by applying certain heat and pressure to the toner image and the printing paper P, and a paper discharging unit 8 discharging the printing paper P having the settled toner image formed thereon.
The paper stacking unit 1 includes a paper cassette having a paper pressing plate supported by an elastic spring elastically urging (biasing) the printing paper P upward.
The paper conveying unit 2 includes a pick-up roller 9 feeding the printing paper P from the paper stacking unit 1 one by one, first and second paper conveying rollers 21 and 22 conveying the printing paper P fed by the pick-up roller 9, and a register roller 23 and a back-up roller 25 aligning the leading end of the printing paper P conveyed from the first and the second paper conveying rollers 21 and 22.
The paper sensing apparatus 30 sensing the leading end of the printing paper P is provided at a downstream side of the register roller 23 on a paper conveying path, which is disposed at a rear side of the register roller 23.
As shown in FIG. 2, the paper sensing apparatus 30 includes a sensor actuator 31 installed on a paper guide frame 24 to be elastically rotated by the printing paper P when the printing paper P is conveyed through the register roller 23 and a photo sensor 33 sensing an end portion of the sensor actuator 31 in accordance with a rotation of the sensor actuator 31 and sending a paper sensing signal to a controlling unit (not shown). The photo sensor 33 includes a light emitting unit emitting light and a light receiving unit receiving the light emitted from the light emitting unit.
The image forming unit 6 includes a photo sensitive drum 3, a developing roller 11 facing the photo sensitive drum 3, a toner supplying roller 13 supplying toner to the developing roller 11, a doctor blade 15 controlling an amount of the toner attached on the developing roller 11, an agitator 17 supplying the toner to the toner supplying roller 13, a toner container 19 storing the toner, and a case 18 provided for the above components to compose a single unit.
A transferring roller 5 is provided at a lower part of the photo sensitive drum 3 installed at the case 18. The settling unit 7 includes a heating roller 26 applying heat to the toner image transferred to the printing paper P from the photo sensitive drum 3 by the transferring roller 5, and a pressing roller 27 pressing the printing paper P against the heating roller 26.
The paper discharging unit 8 includes a paper discharging roller 28 discharging the printing paper P that has been completed with a printing operation, and a paper holder 29 holding and stacking the discharged printing paper P.
An operation of the laser printer 10 having the above structure is as follows. Firstly, the printing paper P is picked up from the paper stacking unit 1 by the pick-up roller 9 and conveyed to the register roller 23 through the first and the second conveying rollers 21 and 22.
The leading end of the printing paper P that has been conveyed to the register roller 23 is aligned by being pushed against a nip between the register roller 23 and the back-up roller 25.
Then, as the printing paper P continues to pass through the nip between the register roller 23 and the back-up roller 25, the leading end of the printing paper P pushes the sensor actuator 31 of the paper sensing apparatus 30 disposed between the register roller 23 and the transferring roller 5. Accordingly, the end portion of the sensor actuator 31 is rotated to be off from the photo sensor 33. As a result, the light receiving unit of the photo sensor 33 receives light from the light emitting unit and sends the paper sensing signal to the controlling unit (not shown).
The controlling unit counts time consumed for the printing paper P to be conveyed from the paper sensing apparatus 30 to the transferring roller 5 in accordance with the paper sensing signal, conveys the printing paper P for a predetermined time, i.e., until the printing paper P reaches a printing operation start position, and then operates the image forming unit 6 and the transferring roller 5.
While the printing paper P is being conveyed to the printing operation starting position, an electrostatic latent image is formed on the photo sensitive drum 3 of the image forming unit 6 by a laser beam reflected through a LSU (laser scanning unit) 4 in accordance with an image signal. The electrostatic latent image formed on the photo sensitive drum 3 is developed to a visible toner image by the developing roller 11.
Then, when the printing paper P reaches the photo sensitive drum 3 of the image forming unit 6, the toner image formed on the photo sensitive drum 3 is transferred to a surface of the printing paper P by the transferring roller 5 in accordance with a control of the controlling unit.
The toner image that has been transferred to the surface of the printing paper P is settled on the surface of the printing paper P by the heat and pressure of the heating roller 26 and the pressing roller 27 as being passed through the settling unit 7. The printing paper P having the toner image settled thereon is discharged to the paper holder 29 formed outside of the laser printer 10 by the paper discharging roller 28 of the paper discharging unit 8.
However, in the above conventional laser printer 10, as shown in FIGS. 3A and 3B, the leading end of the printing paper P is frequently bent due to a friction force or static electricity generated by a contact between the leading end of the printing paper P and the sensor actuator 31 of the paper sensing apparatus 30, and thus there is a problem that a contact point of the sensor actuator 31 and the leading end of the printing paper P is not constantly maintained.
As described above, when the contact point between the sensor actuator 31 and the printing paper P is not regularly maintained, an operation starting time of the paper sensing apparatus 30 becomes unstable. Therefore, the top margin of the printing image printed on the printing paper P also becomes irregular, and as a result, reliability of the laser printer 10 is lowered.
In addition, as shown in FIG. 2, since a distance between an original position and a moving position in which the sensor actuator 31 moves and returns to its original position during sensing the leading end of the printing paper P, is extended, in other words, since an operation range M of the sensor actuator 31 is widened, a distance between the register roller 23 and the transferring roller 5 should be maintained longer than the operation range M of the sensor actuator 31. Therefore, when the distance between the register roller 23 and the transferring roller 5 becomes longer, an error is generated in the laser printer 10 due to a lengthened conveying path of the printing paper P, and accordingly, there is a problem that an accuracy of the top margin of the image printed on the printing paper P is lowered.
The present invention has been made to overcome the above- and/or other problems of the related art. Accordingly, it is an aspect of the present invention to provide a paper sensing apparatus of an office machine, which has a sensor actuator installed to be operated with respect to a rotation center of a register roller in order to reduce a distance between the register roller and a transferring roller and an error generated when sensing a leading end of a sheet of printing paper for the purpose of accurate controlling of a position of a printing image on the sheet.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The above and/or other aspects are accomplished by providing a paper sensing apparatus for controlling a printing position of an image printed by an image forming unit by sensing a leading end of a sheet of printing paper for use in the office machine. The paper sensing apparatus includes a paper stacking unit containing sheets of the printing paper, a pickup unit picking up the printing paper stacked on the paper stacking unit, a conveying unit having at least one conveying roller to convey the printing paper picked up by the pick-up unit and a back-up roller, and an image forming unit forming an image on the printing paper conveyed by the conveying unit. The paper sensing apparatus includes a sensor actuator disposed to pivot with respect to a pivot center of the conveying roller by the printing paper when the printing paper is conveyed, and a sensing unit generating a paper sensing signal in accordance with a rotation of the sensor actuator.
The sensor actuator includes a lever integrally formed with a paper top aligning unit, which is pivotably disposed at a shaft of the conveying roller, to align a leading end of the printing paper. Alternatively, the sensor actuator includes a lever pivotably disposed at the shaft of the conveying roller.
The sensing unit is a photo sensor including a light emitting unit and a light receiving unit.
It is possible that when the paper top aligning unit pivots by the printing paper, the sensor actuator is disposed above the printing paper, and the sensing unit is disposed below the printing paper.
In addition, the sensor actuator operates within a range of 0-5 mm, especially, 1-3 mm after the printing paper enters a nip between the conveying roller and the back-up roller.
The paper top aligning unit includes two supporting members pivotably secured to the shaft of the conveying roller and separated from each other at a predetermined interval, and a connection member connecting the two supporting members and having at least one contact aligning part, which aligns the leading end of the printing paper, integrally formed with the lever of the sensor actuator.
Alternatively, the paper top aligning unit includes, two supporting members pivotably secured to the shaft of the conveying roller and spaced-apart at a predetermined interval from each other, two contact aligning parts integrally formed with two supporting members to align the leading end of the printing paper, and a connection member connecting the two supporting members and having the lever of the sensor actuator integrally formed therewith.